Metallogenesis and Tectonics of the Russian Far East, Alaska, and ...

Chagoyan Stratiforrn Pb-Zn Deposit
The Chagoyan stratiform Pb-Zn deposit (I.G. Khel'vas, written commun., 1963; V.V. Ratkin, this study) consists ofa
galena-sphalerite aggregate which occurs as cement between grains in sandstone. Veinlets are also common. The deposit is about
270 m long and 1.0 m thick, and is hosted in quartz-feldspar sandstone which underlies Cambrian(?) limestone and dolomite.
Galena and sphalerite are the dominant ore minerals, with subordinate pyrite, pyrrhotite, and chalcopyrite. Post-ore dikes and
stocks of Early Cretaceous diorite and granodiorite cut the deposit. The Mesozoic igneous rocks and the contained stratiform ore
bodies !ocally exhibit hydrothermal alteration to quartz, sericite, and tourmaline. The deposit occurs on the northern bank of the
Zeya River and is small. Average grades are 1.42% Pb, 5.16% Zn, and up to 3,000 g/t Ag. The deposit contains estimated reserves
of 65 thousand tomes zinc.
Origin of and Tectonic Controls for
Gar Metallogenic Belts
The rocks hosting the two Gar metallogenic belts are interpreted as forming in a Late Proterozoic volcanic-tectonic basin
in which marine basalt to rhyolite volcanism occurred (V.V. Ratkin, this study). The volcanogenic Fe deposits of the Gar
metallogenic belt consist of sheeted Fe layers, mainly magnetite, which are hosted in metamorphosed Early Cambrian(?) felsic and
mafic volcanic rocks and limestone. The stratiform Cu and Pb-Zn deposits of the Gar metallogenic belt are hosted in Cambrian
rhyolite (Cu deposits) and quartz-feldspar sandstone (Pb-Zn deposits) which underlies Cambrian(?) basalt and calcareous rocks.
These stratified units comprise part of the Mamyn continental-margin arc terrane (fig. 2). Tbese stratigraphic units and stratiform
deposits are (Nokleberg and others, 1994c, 1997~): (1) underlain by Archean(?) gneiss and schist, granite-gneiss, gabbro, and
amphibolite which exhibit granulite facies metamorphism, and Proterozoic(?) and Early Cambrian sequence consists of
greenschist, metasandstone, marble, quartzite, felsites, sandstone, and siltstone; and (2) are overlain by Silurian clastic rocks and
Middle Devonian siltstone, sandstone, and limestone which are gently folded. The tectonic origins of the stratiform sulfide
deposits are poorly understood and need further study.
Metallogenic Belts Formed During
Early Paleozoic Sea-Floor Spreading,
Regional Metamorphism, or During
Subduction-Related Volcanism in
Russian Far East Terranes
Galarn Metallogenic Bett of Volcanogenic Fe,
Volcanogenic Mn, and Sedimentary P Deposits (Belt GL)
Central Part of Russian Far East
The Galam metallogenic belt of volcanogenic Fe, volcanogenic Mn, and sedimentary P deposits (fig. 2; tables 3,4)
occurs in the central part of the Russian Far East in the Galam accretionary wedge terrane (Shkolnik, 1973). The significant
deposit is the Gerbikanskoe volcanogenic Fe deposit; other deposits are: the North-Shantarskoe, Nelkanskoe. Ir-Nimiiskoe-2, and
Lagapskoe sedimentary P deposits; and the Ir-Nimiiskoe- 1, Milkanskoe, Galamskoe, Gerbikanskoe, Kurumskoe, and Itmatinskoe
volcanogenic Fe and Mn deposits (table 4) (Nokleberg and others 1997a, b, 1998). The Fe and Mn deposits occur in Cambrian
beds and lenses with chert in seafloor basins and are interpreted as forming during seafloor hydrothermal activity which was
associated with mafic volcanism.
The sedimentary P deposits are phosphorites which formed in limestone caps which formed in two stages on accreted
seamounts, atolls, and guyots. The older stage consisted of siliceous deposition of phosphate coquina (inarticulate brachiopods,
trilobites, etc) in the section of those atolls. Abrasion resulted in the formation of fragmentary trains, including phosphorite
fragments. The younger stage consists of accumulations of phosphorite fragments. The deposits are interpreted as being
subsequently deformed and metamorphosed during subsequent accretion of the Galam terrane.
Gerbikanskoe Volcanogenic Fe Deposit
The Gerbikanskoe volcanogenic Fe deposit (fig. 10) (Shkolnik, 1973) consists of two zones separated by a sequence of
sandstone and siltstone. The two zones contain approximately 30 steeply-dipping sheets and lenses of magnetite and hematite.
Individual bodies are several tens of m to 5 to 7 km long, and locally occur in a closely-spaced en-echelon pattern. Thickness
varies from 5 to 50 m and is commonly 8 to 28 m. Fe-rich zones vary from banded to thinly-banded, lenticular-banded, and
bedded, and consists of finely-dispersed hematite, magnetite, and rare pyrite and chalcopyrite. The deposit is large with an average
grade of 42-43% Fe (soluble Fe 33-53%); 1.8% Mn, and 9.6% P.